This laboratory has been investigating methods for determining infarct size and for preserving myocardium following acute coronary ligation in baboons for several years. The present studies are designed to: 1) Verify the accuracy of two clinically applicable methods of sizing an acute myocardial infarct (AMI): a) Precordial ECG maps have become a standard method of assessing efficacy of post AMI therapeutic intervention in preserving myocardium. The accuracy of this technique has not been validated in the laboratory and will be undertaken in the standard AMI model we have developed in baboons. b) Recent investigations have demonstrated the accuracy of vectorcardiography taken 6 hours to 10 days post AMI in measuring infarct size in baboons. No data is available on the usefulness of vectors at earlier or later time periods in following the evolution of an infarct or as a possible tool for evaluating efficacy of therapeutic interventions. 2) Characterize the role of collateral circulation in our model in primated. We have seen marked species differences in infarct configuration which need to be understood to fully assess the applicability of studying intervention effectiveness in different animal models.